含氮穿隧氧化層再氧化行為於氮化矽快閃式記憶體之特性與研究

Abstract

在我們的實驗中，因為傳統的氧化層在寫入和抹除期間，矽基板和穿隧氧化層的接面處可能由於電性應力誘發漏電流造成界面陷阱密度增加，所以我們使用含氮氧化層當作穿隧氧化層。由於在氮化矽電荷捕捉層中較淺的陷阱密度是非常高的，這些較淺的陷阱將造成儲存於氮化矽電荷捕捉層中的電子跳躍來移動，這就是所謂的跳躍傳導。被儲存的電子可能藉由跳躍傳導而跑到靠近穿隧氧化層，因此這些電子將會有較高的機率去穿透過穿隧氧化層。因此在氮化矽中較淺的陷阱將導致電荷保存度下降。所以我們採用在氮化矽電荷捕捉層被沉積之後做在氧化的動作去產生雙極性深的陷阱≣Si─Si≣，它將有效的去改善資料保存度的特性。而且這些深的陷阱是有幫助的對於去改善電子由於熱能被激發的現象。然後，使用傳統熱氧化層來當作上氧化層其和氮化矽相接的能帶是平滑的。因此載子是較容易去穿透上氧化層，並且對上氧化層造成傷害，導致那耐操度的特性下降。然而，使用化學氣相沉積四氧乙基矽酯的上氧化層和氮化矽相接的能帶是陡峭的。載子將不易穿隧過上氧化層，進而改善耐操度的特性。因此我們採取化學氣相沉積四氧乙基矽酯的氧化層來當作我們的上氧化層。而且我們發現在化學氣相沉積四氧乙基矽酯的氧化層形成之後做緻密化的處理也可以改善資料保存度的特性。

In out experiment, we used the oxynitride as the tunneling oxide because the stress induced leakage current may cause the increase of interface-trap density between silicon substrate and tunneling oxide during the programming and erasing cycles for convention oxide. Due to the shallow trap density in silicon nitride trapping layer is very high, this will cause the electrons stored in trapping layer jump by these shallow traps, which is so-called hopping conduction. The electron stored may jump near tunneling oxide and have the higher probability to tunnel through tunneling oxide. Hence, these shallow traps in silicon nitride will result in the degradation of retention characteristics. Therefore, we adopt the reoxidation process after the silicon nitride trapping layer deposited to produce the amphoteric deep trap “≣Si─Si≣”, and it is effective to improve the characteristics of data retention. Furthermore, these deep traps assist to improve the phenomenon of thermal assisted tunneling. Then, the energy band of blocking oxide connecting with nitride for the conventional SONOS structure is smooth. Hence, the carrier tunnel easily across blocking oxide and it will harm the blocking oxide to cause the degradation of endurance characteristics. However, the energy band of blocking oxide connecting with nitride for using CVD TEOS oxide as blocking oxide is steep. The carriers will not tunnel through blocking oxide easily, and that can improve the characteristics of endurance. Therefore, we adopt the CVD TEOS as blocking oxide. We can find the densify after CVD TEOS deposited will also improve the characteristics of data retention.